Non-linear transmission lines support shock waves and electrical solitons, as has been known theoretically and demonstrated experimentally. FIG. 1A shows a periodic structure 100 made up of a non-linear waveguide comprising a transmission line consisting of a pair of conductors 102,104 loaded with varactor diodes 106 implementable in gallium arsenide (GaAs) technology and demonstrated to compress the fall time of a sinusoidal microwave signal. The varactor diodes 106 are separated by plurality of transmission line segments 112 of approximately equal line lengths or period d. A DC power supply 116 provides reverse bias to the varactor diodes 106. A signal generator 108, one node of which is grounded, supplies a generally sinusoidal input voltage signal 190 with a typical waveform as shown in FIG. 1B to the non-linear transmission line. The signal generator 108 has source impedance represented by a resistor 114. A load 110 is connected to receive a resultant output signal 192 shaped by the varactor-loaded transmission line, a typical waveform of which is shown in FIG. 1B.
FIG. 2A shows a periodic structure 200 made up of a non-linear waveguide comprising a transmission line consisting of a pair of conductors 202,204 loaded with varactor diodes 206 implemented in gallium arsenide (GaAs) technology and demonstrated to compress the rise time of a sinusoidal microwave signal. The varactor diodes 206 are separated by plurality of transmission line segments 212 of approximately equal line lengths or period d. A DC power supply 218 provides reverse bias to the varactor diodes 206. An input signal 290 and resultant output signal 292 are shown in FIG. 2B.
U.S. Pat. No. 5,789,994 to Case et al. teaches a non-linear waveguide employing a pair of transmission lines loaded with anti-parallel varactor diodes used to simultaneously compress the rise and fall times of a sinusoidal signal. The conversion efficiency of the circuit is lower than that of a purely reactive non-linear transmission line because the anti-parallel arrangement of one set of varactor diodes is reverse biased (reactive non-linearity) while the other set of varactor diodes is forward biased (resistive non-linearity).
In another approach, heterostructure barrier varactor diodes (HBV) having a symmetric C-V characteristic are used to generate odd-frequency harmonics (i.e. a square wave). However, self heating caused by the conduction current through the bulk of the varactor diodes results in reduced conversion efficiency. In addition, the unconventional epitaxy of HBV diodes can make their integration with other common processes (e.g. PHEMT, HBT) difficult.